Use of xylene in controlling melt flow of modified polyolefin compositions

ABSTRACT

IN MODIFIED POLYOLEFIN COMPOSITION PREPARED BY REACTING AN OLEFIN POLYMER WITH A POLYMERIZABLE COMPOUND GENERALLY DEFINED BY   CH2=C(-R3)-(R4)(0-1)-SI(-R5)3   IN THE PRESENCE OF AN ORGAIC PEROXIDE, THE MELT FLOW MAY BE CONTROLLED BY INCLUDING IN THE REACTION MIXTURE A QUANTITY OF XYLENE. THE REACTION PRODUCT IS PARTICULARLY SUITED FOR REINFORCEMENT WITH FILAMENTARY MATERIAL OR AS A COATING ON METALLIC SURFACES.

United States Patent USE OF XYLENE IN CONTROLLING MELT FLOW OF MODIFIED POLYOLEFIN COMPOSITIONS Albert Schrage, East Orange, and Philip D. Readio, Sparta, N.J., assignors to Dart Industries Inc., Los Angeles, Calif.

No Drawing. Continuation-impart of application Ser. No. 177,143, Sept. 1, 1971, now Patent No. 3,755,495, which is a division of applications Ser. No. 81,526, Oct. 16, 1970, now Patent No. 3,696,169, and Ser. No. 253,090, May 15, 1972, now abandoned, which in turn is a division of application Ser. No. 129,623, Mar. 30, 1971, both now abandoned. This application Apr. 9, 1973, Ser. No. 349,592

Int. Cl. C08f 29/12, 35/06 US. Cl. 260-827 Claims ABSTRACT OF THE DISCLOSURE Si )a in the presence of an organic peroxide, the melt flow may be controlled by including in the reaction mixture a quantity of xylene. The reaction product is particularly suited for reinforcement with filamentary material or as a coating on metallic surfaces.

This application is a continuation-in-part of pending applications, Ser. No. 177,143, filed Sept. 1, 1971, now US. Pat. No. 3,755,495, which is a division of Ser. No. 81,526, filed Oct. 16, 1970, now US. Pat. No. 3,696,169, and Ser. No. 253,090, filed May 15, 1972, now abandoned which is a division of Ser. No. 129,623, filed Mar. 30, 1971, now abandoned.

This invention relates to improvements in modified polyolefin compositions having good adhesiveness characteristics and methods for their preparation.

Modified polyolefin compositions having good adhesiveness characteristics, particularly toward polar materials, are described in application Ser. No. 81,526, filed Oct. 16, 1970. These compositions are formed, in general, by reacting an olefin polymer with certainethylenically unsaturated polymerizable compounds in the presence of an organic peroxide. While the resulting modified polyolefin compositions exhibit adhesiveness characteristics which are far superior to the unmodified polyolefins the melt flow of the compositions is undesirably high. As is well known, polymers having undesirably high melt flow values also undergo a reduction in physical properties such as tensile strength, flexural strength and impact strength.

This invention provides a solution to the problem of unduly high melt flow in these modified polyolefin compositions. Briefly, the invention involves the use of xylene in the reaction of the olefin polymer with the ethylenical- 1y unsaturated polymerizable compound in the presence of the organic peroxide. Xylene is merely charged along with the other reactants to a reactor and the entire mixture is subjected to the usual polymerization conditions. The resulting modified polyolefin compositions have far lower melt flow values than such compositions prepared without the use of xylene.

Briefly described, modified polyolefin compositions of this invention are produced by the process comprising providing an olefin polymer derived from alpha-olefin monomers having 2 to 10 carbon atoms in particulate form; admixing the particulate olefin polymer with xylene,

3,830,872 Patented Aug. 20, 1974 r'rlce organic peroxide and a polymerizable compound defined y I'R3 3 CH1 0 \R/HIS1(R) wherein R R and R are hereinafter defined; reacting the resulting mixture at a temperature below the tacky point of the polymer; and recovering a modified polyolefin composition directly from the reaction in particulate form. Various advantages are achieved with this process among which is included the production of a modified polyolefin composition having improved melt flow and adhesiveness characteristics directly in particulate form. Since the re action is conducted without the necessity of melting the polymer there is no requirement for comminuting or grinding the product to obtain a free-flowing particulate product. Moreover, it is believed that a more uniformly modified composition is obtained from the process due to the high total surface area of the polymer exposed dur ing the reaction as well as the ability to obtain intimate mixing of the ingredients.

The polyolefins suitable for use in the process are those derived from alpha-olefin monomers having 2 to 10 carbon atoms. Included among these are polyethylene, polypropylene, poly(butene-1), poly(4 methyl-pentene 1), ethylene-propylene copolymers, and terpolymers of ethylene-propylene-butene-l.

As mentioned above, in accordance with this invention, these polyolefins are in particulate form such as powders, granules, chips, pellets, and the like, all of which are commercially available. Powdered polyolefins are preferred as the greatest surface area is thus obtained. Powders having an average particle size in the range of about 0.001 mm. to about 4 mm. are particularly preferred, more preferably 0.01 to 1 mm. The use of powdered polyolefins is a specific feature of the process of this invention since such powders are inherently produced in certain olefin polymerization processes, most notably polypropylene and polyethylene. Thus, the process of this invention may easily be incorporated in such olefin polymerization processes as an optional sequence of steps to provide an additional capability ofproducing the modified polyolefin compositions with a minimum of additional equipment.

The polymerizable compounds are those compounds defined by -(O C alkylene) O0- group with or without pendant glycidoxy groups; a

C-O(C1C1o alkylene)- group with or without pendant glycidoxy groups; or a group; a

group with or without pendant glycidoxy groups; and

R is halogen, bromine or chlorine in particular, an alkoxy radical having 1 to carbon atoms, or an acyloxy radical having 1 to 10 carbon atoms.

Preferably, R is either absent or a C -C alkylene group and R and R are as described above.

Included within the above defined group of compounds are the following by structure Such compounds are commercially available.

The organic peroxides useful in the process of this invention include both solid and liquid organic peroxides. In order to insure good distribution of the peroxide throughout the mixture of ingredients prior to reaction it is preferred to use a liquid form of the peroxide. Thus, for convenience, those organic peroxides which are normally liquid or which become liquid at or near the temperature at which the particular reaction is run are preferred over the solid-type organic peroxides. However, by dissolving the solid organic peroxides in a suitable organic solvent, that is one that has no substantial adverse effect on free radical polymerization reactions, a suitable physical form is obtained which can be used with substantially equal success in the process of the invention. Since the solvent, for this purpose, merely functions as a carrier for the solid organic peroxide it makes no difierence whether or not it becomes vaporized prior to reaching reaction temperature since the peroxide at that point in the process has already been distributed throughout the ingredients.

Some examples of suitable peroxides include di-t-butyl peroxide, t-butyl hydroperoxide, methyl ethyl ketone peroxide, t-butyl perbenzoate, t-butyl peracetate, t-butyl peroxypivalate, acetyl peroxide, t-butyl peroctoate, t-butyl peroxyisobutyrate, decanoyl peroxide, lauroyl peroxide, benzoyl peroxide, 2,5-dimethylhexane 2,5 diperoxybenzoate, cyclohexanone peroxide, cumene hydroperoxide, pmenthane hydroperoxide, di t butyl-diperoxyphthalate, cumyl peroxide, caproyl peroxide, and the like. Of course, there are additional organic peroxides in this group but are too numerous to attempt to individually name. As mentioned previously, it is preferred that the organic .peroxide be in a liquid form or capable of dissolution in a substantially inert organic solvent at or near the temperature at which the particular reaction is carried out.

Selection of a particular organic peroxide or mixture of organic peroxides of the type mentioned above may be easily determined based on the temperature at which the particular reaction is to be carried out and the corresponding decomposition rate of the peroxides as evidenced by their respective half-lives. The half-lives of peroxides are well known and may be readily ascertained (see U.S. 3,293,233).

It is pointed out that oxygen preferably should not be employed in the process even though it is sometimes regarded as a free radical initiator. Oxygen is known to cause deleterious effects on polymerizable monomers (see page 36 of the reprint of Chapters I-IV from Monomeric Acrylic Esters by E. H. Riddle, 1954). Since oxygen has some adverse effect on the reaction it is desirable to conduct the reaction in a substantially oxygen-free atmosphere if possible. While small amounts of oxygen can probably be tolerated in the system effort should be made to prevent introduction of additional oxygen over and above what may be initially present. Preferably, the reactor is purged with an inert gas prior to conducting the reaction.

The xylene is added to the olefin polymer particles prior to reaction and is evenly distributed throughout. Preferably, 0.01 to 10 percent by weight of xylene based on the olefin polymer are employed. This amount does not visually appear to change the dry nature of the mixture of ingredients prior to reaction. It is not known as to just how the minor amount of xylene functions in the process. In any event, whatever the mechanism, the result is a desirable reduction in melt flow and further enhancement of the bonding ability of the modified composition as evidenced by an increase in flexural strength of glass fiber reinforcement of the compositions. The most significant increases are obtained when at least 0.5 part by weight of the polymerizable compound is employed.

As described previously, in accordance with the process of the invention, the above ingredients, that is the olefin polymer in particulate form, the polymerizable compound, the xylene and the organic peroxide, are admixed on a substantially dry basis. The amount of liquid is insufiicient to cause any discernible change in the dry-appearance of the mixture.

The admixing of the ingredients may be accomplished by merely charging the ingredients, separately or simultaneously to a mixing apparatus such as a Henschel mixer. After achieving homogenization of the ingredients in the mixer the mixer is transferred to a reaction zone for reaction as hereinafter described. Rather than separately mixing the ingredients remote from the reaction they may also be charged directly to a reactor equipped with some means for agitation or tumbling to achieve homogenization of the ingredients within the reaction zone.

In any event, once the mixture is present in the reaction zone, the zone is preferably purged of any oxygen with an inert gas and the reaction is conducted at a temperature which is below the tacky point of the olefin poly mer to avoid agglomeration of the polymer particles. The tacky point of the olefin polymer is defined as that temperature at which the surfaces of the polymer particles become sufiiciently soft so as to be tacky and tend to stick to one another and to other surfaces. Preferably, some mild agitation is provided to insure good heat transfer and help to maintain the homogeneity of the mixture during reaction. The precise temperature at which the reaction will be carried out will vary depending on the specific olefin polymer, the specific polymerizable compound and the specific organic peroxide or peroxide mixture employed. Generally, it will be somewhere in the range of 0 C. up to below the tacky point of the olefin polymer. For polypropylene the upper temperature limit will be about 150 C., for high density polyethylene (e.g. 0.930 and above) it will be about 120 C. and for low density polyethylene (e.g. below 0.930) it will be about C. Thus, it is apparent that the upper temperature limit will vary considerably depending on the particular polymer.

The pressure at which the reaction is conducted is not critical and, in general, good results can be obtained at pressures in the range of atmospheric up to about 1000 p.s.i. For practical reasons it is convenient to operate from about atmospheric up to about 200 psi. and under conditions to assure that the xylene is maintained in the reaction zone. As indicated previously, the reaction zone is usually purged with an inert gas to remove any oxygen prior to conducting the reaction. In some instances it may be convenient to merely close the system and begin the reaction whereby an autogenous pressure is built up and maintained. In other instances it may be convenient to close the system and pressurize the reaction zone with the inert gas, e.g. carbon dioxide, nitrogen, argon, etc. in order to prevent excessive volatilization of volatile ingredients.

The reaction zone may be of a fluid bed type wherein the admixed ingredients are charged to form the bed. The system is then preferably purged with the inert gas to remove oxygen and closed. An externally heated inert gas is then continuously circulated through the bed as is known in these systems and the reaction proceeds. The movement of the inert gas through the bed conveniently provides agitation sufiicient to aid heat transfer and maintain the homogeneity.

In a variation of the above described fluid bed reaction, it is also possible to form the bed solely from the olefin polymer particles and inject the necessary quantities of the polymerizable compound, xylene and organic peroxide, either separately or as a mixture, into the heated gas stream prior to its passage through the bed of polymer particles. In this manner, the flow of the gas stream serves to agitate the polymer particles and uniformly distribute the polymerizable compound, xylene and organic peroxide throughout the particles as the reaction proceeds.

Another type of reaction zone for conducting the process of this invention is provided by a vessel equipped with helical ribbons. With this system it is not necessary to separately mix the ingredients and then charge them to the vessel as the ribbons in the vessel will adequately mix the materials when separately charged. Heating of the mixture is accomplished through external jacketed heating means. The ribbons function to aid heat transfer and maintain good mixing of the ingredients.

In conducting the reaction it is desirable to completely decompose the organic peroxide before recovering the product as the presence of any residual peroxide, even in small quantities, may adversely affect the resulting composition in subsequent compounding, molding or extruding operations.

The resulting modified polyolefin composition may be easily recovered directly from the reaction zone in particle form and thus is suitable for subsequent operations as mentioned above without any further steps such as comminuting. The composition exhibits increased bonding with such materials as glass, particularly glass fibers used in reinforcing compositions of this type.

The reaction product, that is the resulting composition of this invention is particularly suited for reinforcement with filamentary material such as glass fibers or asbestos in amounts ranging from about 5 to 90% by weight. Such reinforced compositions may be produced in accordance with conventional techniques, see US. 3,416,990, US. 3,453,356, and US. 3,042,570. In addition, the reaction product is useful in coating surfaces, e.g. metallic or glass containers and the like, due to the adhesiveness properties it possesses.

Other additives may be incorporated in the reaction product including fillers, pigments, stabilizers, anti-oxidants, anti-static agents, flame retardants and the like.

The following example will serve to further illustrate the invention.

EXAMPLE I A series of compositions were prepared according to the method set forth below. A mixture comprising 100 parts by weight polypropylene particles (average size in the range of 0.01 mm. to 4 mm.), 0.2 part by Weight 7- methacryloxypropyl trimethoxy silane, 0.5 part by weight t-butyl peracetate (75% solution in benzene) and 2.0 part by weight xylene were mixed in a Waring Blender and charged to a reactor with a paddle stirrer. The dry-appearing free-flowing mixture was stirred to distribute the materials while first purging the system with argon and then heating to about 125 C. under autogenous pressure; The mixture was maintained at about 125 C. for about 4 hours while continuing the stirring and then cooled and subjected to vacuum to remove any volatiles present. The

resulting composition was recovered directly from-the reactor in a particulate form. H

For comparison, a second series of compositions were prepared using the same procedure except that no xylene was employed. The products were recovered in a particulate form.

Each of the above compositions was tested for melt flow (230 C.) in accordance with ASTM D-1238 and then blended with 20 weight percent chopped glass fibers inch, OCF 885) for testing for flexural strength and flexural modulus properties in accordance with ASTM D- 790-66. The results of these evaluations are indicated in the following table.

TABLE I Xylene Flexural (parts Flexural modulus by Melt strength (p.s.i. Sample number weight) flow (p.s.i (X10 Thus, having described the invention in detail it will be understood by those skilled in the art that certain variations and modifications may be made without departing from the spirit and scope of the invention as described herein or in the appended claims.

What we claim is:

1. A process for preparing a modified polyolefin composition having improved melt fiow characteristics which comprises: I

(a) providing an olefin polymer in particulate form, said olefin polymer being derived from alpha-olefin monomers having 2 to 10 carbon atoms,

(b) admixing the olefin polymer in particulate form with an organic peroxide, from 0.01 to 10 percent based on the weight of the olefin polymer of xylene and from 0.01 to 10 percent based on the weight of the olefin polymer of a polymerizable compound to provide a substantially dry mixture, said polymerizable compound being defined by wherein R is hydrogen or an alkyl radical having 1 to 4 carbon atoms;

R is a straight, branched or cyclic al kylene radical having 1 to 10 carbon atoms with or without pendant glycidoxy groups; a substituted or unsubstituted phenylene group with or without pendant glycidoxy groups; a

group; a

-(C1Gm alkyleneJ-(flJ-O- group with or without pendant glycidoxy groups; a

?O(C 1-0 m alkelene) group with or without pendant glycidoxy groups; or a 0 (C -C alkylenekli-O-(C r0 alkylene) group with or without pendant glycidoxy groups; and R is halogen, an alkoxy radical having 1 to 10 carbon atoms, or an acyloxy radical having 1 to 10 carbon atoms; (c) reacting the resulting mixture in a reaction zone at a temperature below the tacky point of the olefin polymer and at a pressure sufficient to maintain the References Cited xylene within the reaction zone, and UNITED STATES PATENTS (d) recovering a modified polyolefin composition directly from the reaction in particulate form. 3,075,948 1/1963 Santenl 260-327 2. A process according to Claim 1, wherein 5 3,505,279 4/1970 Preston et a1. 260-827 3 i H or a CFC1 alkyl group, 3,573,334 3/ 1971 Whe ler 260827 R* is either absent or a 0 -0 alkylene group, and 3,644,245 2/1972 Flanagan at 260827 R is bromine, chlorine, a C -C alkoxy group or a 3,644,141 2/1972 Preston 260-827 3,646,155 2/1972 Scott 260827 C -C acyloxy group.

3. A process according to Claim 1 wherein the re- 10 action is conducted in the absence of oxygen. WILBERT S, SR., Primary Examiner 4. A process according to Claim 1, wherein the U S 01 X R polymerizable compound is 'y-methacryloxypropyl trimethoxy silage, 117-124 E, 132 BS; 260-33.6 SB, 33.6 PQ, 878

5. A process according to Claim 1, wherein the olefin 15 polymer is polypropylene, polyethylene or a copolymer of ethylene and propylene. 

